Effect of prenatal betamethasone administration on maternal and fetal corticosteroid-binding globulin concentrations

OBJECTIVE: This study was undertaken to examine the effects of prenatal bet amethasone administration on corticosteroid-binding globulin concentrations in maternal and fetal plasma and amniotic fluid. STUDY DESIGN: Two groups of patients with preterm labor at 24 to 35 weeks' gestation who were receiving prenatal betamethasone (2 intramuscular doses of 12 mg) were studied. Maternal plasma was obtained before and at variable intervals until 1 week after betamethasone administration. Umbilical cord blood and amniotic fluid samples were collected at the time of delivery. Sa mples were also collected from patients at risk for preterm delivery who di d not receive glucocorticoids. RESULTS: Betamethasone suppressed maternal cortisol concentration by >70% w ithin 24 hours of injection but did not significantly alter corticosteroid- binding capacity or relative concentrations of corticosteroid-binding globu lin isoforms in either maternal or umbilical cord plasma. Betamethasone red uced corticosteroid-binding capacity in amniotic fluid within 24 hours of i njection, and values remained suppressed 1 week after treatment. CONCLUSION: Maternal and fetal plasma corticosteroid-binding globulin conce ntrations were unchanged after maternal betamethasone administration at 24 to 32 weeks' gestation but amniotic fluid corticosteroid-binding globulin c oncentrations decreased significantly, suggesting different sites of either corticosteroid-binding globulin production or regulation or both.